1. Field of the Invention
The present invention generally relates to communication systems and, more particularly, to a method and apparatus for detecting the presence of a wireless local area network.
2. Description of the Related Art
Presently, 2.5 generation (2.5G) and third generation (3G) cellular networks can provide wireless data service, such as wireless Internet service, having data rates up to 2 Mbps. On the other hand, wireless local area networks (WLANs), such as IEEE 802.11a, IEEE 802.11b, and HiperLAN/2 wireless networks, for example, can provide data service with rates higher than 10 Mbps. WLAN service is also typically cheaper to implement than cellular service due to the use of unlicensed frequency bands by WLANs. As such, it is desirable to switch from cellular service to WLAN service when a mobile device is within the service area of a WLAN. Switching between cellular service and WLAN service can provide for optimal utilization of the available spectrum, and can reduce the burden on cellular networks during times of peak activity.
Mobile devices typically have limited power resources. Continuously checking for the presence of a WLAN by powering up a complete WLAN subsystem can result in considerable power drain. Thus, there is a need to minimize power used by mobile devices capable of communicating with multiple types of wireless networks, such as cellular and WLAN networks.
The present invention is a method and apparatus for indicating the presence of a wireless local area network (WLAN). Specifically, the present invention detects at least one signature sequence in a radio frequency (RF) signal associated with a WLAN. In one embodiment, the present invention filters samples of the RF signal to correlation the RF signal with a stored signature sequence indicative of a WLAN. The correlated RF signal is then coupled to a peak detector for sensing at least one peak therein. The present invention indicates the presence of a WLAN in response to the detection of the at least one signature sequence in the RF signal.